When planting seeds, in particular for large scale applications such as a commercial farm, a ground engaging apparatus such as a planter apparatus may be towed behind a tractor to cut channels or furrows into the soil which is followed by planting of a seed within the channel. Usually, a plurality of planter units are attached to a support towing bar that aligns the planter units at selected distances apart from each and the support bar is attachable to a tractor via a tow bar.
The ground engaging unit may comprise a frame having a pivotable parallelogram arrangement that maintains a ground opening tool in the ground while traversing level and uneven ground. A spring located between two pivotable arms of the parallelogram applies a force that maintains the ground opening tool at a pre-selected depth in the soil as the ground engaging unit encounters inclines and depressions. When the ground engaging unit encounters an obstacle such as a rock or stump, the shank is pivoted upward and away from the obstacle by a break-away or breakout mechanism to thereby prevent damage to the ground opening tool. The break-away mechanism comprises a spring that applies a force independent of the parallelogram as a separate break-away unit.
A ground engaging apparatus described in Australian patent AU 1996 60854 B2 (714157) (Techsearch Incorporated) comprises a single bias means for adjusting both a downward force to maintain the ground opening tool in the soil at a selected depth and a break-away force that maintains the ground opening tool in the soil unless the planter unit encounters an obstacle. This design is limited in that adjusting the downward force on a parallelogram arrangement also adjusts the break-away force, which is undesirable in situation where a user wishes to adjust each force independently of the other. Also, a minor adjustment of the bias means to the downward force of the parallelogram has a significant affect on the break-away force, which may result in excessive break-away force applied to the ground opening tool.